Phosphors are used in fluorescent tubes, fluorescent display tubes, luminous display boards, and the like, and application of phosphors has been increasing. In recent years, attempts are made to use a phosphor in combination with an LED in various display apparatuses including TV monitors. Furthermore, white phosphors, which are expected to be applicable to a wide variety of fields, have actively been studied and developed.
There are various organic and inorganic fluorescent materials for use as a raw material of a phosphor, including natural fluorescent materials. Using such fluorescent materials as a raw material, various research and development have been conducted in an attempt to provide desired emission colors of phosphors, improvement in peak intensity of emission spectra or, economic efficiency of phosphors and the like.
As a result of such research and development, new phosphors and methods of producing the same have been reported in recent years.
For example, Patent Document 1 discloses a phosphor represented by the general formula MmAaBbOoNn:Z (wherein M is one or more elements having a valency of II; A is one or more elements having a valency of III; B is one or more elements including at least Si and having a valency of IV; O is oxygen; N is nitrogen; Z is one or more activator agents; m>0; a>0; b>0; o≧0; and n>0.). Regarding a method of producing the above-described phosphor, Patent Document 1 describes that when the phosphor is obtained by firing a predetermined mixture in a firing furnace, it is desirable to perform the firing of the mixture at least twice and to grind and mix the fired mixture between the firing steps, and also that repetition of the firing step provides an improvement in uniformity of the fired product and emission efficiency of the phosphor.
Patent Document 2 discloses a monoclinic phosphor mainly composed of an inorganic compound in which metal element M (wherein M is one or two or more elements selected from Mn, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) forms a solid solution with a host crystal represented by AxSiyN (2/3x+4/3y) (0<x<2, y=2-x) (wherein A is one or two or more elements selected from Mg, Ca, Sr and Ba). Regarding a production method of the monoclinic phosphor, Patent Document 2 describes that when aggregate powders obtained by firing adhere firmly to one another, it is desirable to grind the aggregate powders by use of a grinder to reduce their average particle size to 20 μm or smaller and thereafter to subject the powders to thermal treatment at a temperature of 1000° C. or higher, whereby the surface state of the fired product, which has been degraded during the grinding and the like, can be ameliorated to improve brightness of the phosphor.
Patent Document 3 discloses a method of producing a phosphor in which the phosphor precursor, which is prepared by thermal solidification of a mixed melt comprising combination of a metal compound containing at least one metal selected from the group consisting of Al, B, Ba, Be, Bi, Ca, Cd, Cs, Ga, Ge, Hf, In, K, Li, Mg, Mo, Nb, P, Rb, Si, Sn, Sr, Ta, Ti, V, W, Zr and rare earth metals with carbamide and/or carbamide derivative, is ground and then fired to produce the desired phosphor. Carbamide and the like are decomposed into a resin component during the process of preparing the precursor. This resin component facilitates grinding treatment of the precursor. Once the precursor is subjected to the subsequent firing step, the resin component disappears completely. Accordingly, components derived from carbamide and the like would not remain in the final phosphor product.
Patent Document 4 discloses an M-C-N-O based phosphor comprising a group IIIB element (M), carbon (C), nitrogen (N) and oxygen (O) and a method for producing the same, in which boron (B) is used as the group IIIB element and a solution of a mixture comprising boric acid, carbamide, and a polymer is fired.